This ended up as a double post when the type box repeatedly went blank when I tried to edit and click on Preview Post. The type inside the box would appear when I backtracked one page, but then it double posted instead of making the change in the original.
This happened yesterday as well, but I thought it a one-time glitch. However, another poster later remarked upon it that same day. It might be a developing problem.
It’s occurred to me twice recently, and I don’t know of any significant changes to my setup. I am going to try and edit this post to see if it happens again.